Photoelectrochemical properties of TiO2 photocatalyst and its applications for environmental purification

In view of the situation that environmental issues become more serious day by day, recent studies on practical applications of TiO₂ photocatalysis for environmental purification are reviewed. Although the fundamental aspects and the mechanisms of TiO₂ photocatalysis have recently become quite well understood, effective photocatalytic environmental purifier, especially water purifier, could not be developed to the stage of real industrial technology. The removal rate of gaseous or aqueous contaminants is influenced by numerous parameters; UV light intensity, substrate concentration, O₂ partial pressure, humidity, substrate type, and so on. Moreover, TiO₂ photocatalyst essentially has a difficulty in decomposition of large amount of contaminants or refractory chemicals. As the solutions of these problems, combination with other processes such as advanced oxidation processes and improvement of the design of photocatalytic environmental purification systems are described. During the past several years, the strategies for effective design of the system are well discussed and evaluated. The reactor design for air- or water-purification can be classified into two main strategies: (1) enlargement of reactive surface area and (2) improvement of mass transfer. Based on these insights, very recent achievements for development of photocatalytic environmental purification system with our contribution in each aspect and future research directions are reviewed.     

Carboxylic acid recognition of diamidine having a fluorescent 1,8-diphenylanthracene unit and its detection of amidinium-carboxylate and amidinium formation

A diphenylanthracene-based diamidine (1a) fluorescent probe for the detection of dicarboxylic acids has been designed and synthesized, which has an extended π-conjugation rather than a simple anthracene ring, in order to observe highly different fluorescence wavelengths after complex formation with dicarboxylic acids. The fluorescence spectra of the mixed solution of the diamidine 1a and carboxylic acids showed two different fluorescence bands, which corresponded to the complex formation (amidinium-carboxylate formation, λ_em?=?450?nm, light blue color) and dissociated amidinium formation (λ_em?=?510?nm as a broad band, green color). The complexed and dissociated states were confirmed by DOSY NMR and TD-DFT calculations. These different fluorescence wavelengths may come from the differences in the dihedral angles between the phenyl rings at the 1,8-position and anthracene ring (difference in π-conjugation) of 1a under complex formation and dissociated amidinium formation. The proposed mechanism for the observation of the different fluorescence wavelengths (complex formation and amidinium formation) was also confirmed by the fluorescence study of diamidine 1b which causes restricted rotation of the phenyl rings by substitution of the steric methyl groups, and observed the same fluorescence spectra for the complex formation and amidinium formation (400, 420, 450?nm as a vibrational structure of anthracene ring). These fluorescence characteristics of the diamidine 1a are also applicable for the detection of α,ω?dicarboxylic acids.     

Mössbauer spectroscopic study of photo-sensitive organic–inorganic hybrid system, (SP)[Fe(II)Fe(III)(dto)3](dto = C2O2S2, SP = spiropyran)

A photo-sensitive organic–inorganic hybrid system (SP)[Fe^IIFe^III(dto)₃] (SP = spiropyran, dto = C₂O₂S₂), has recently been developed, where the photo-isomerization of the intercalated spiropyran in solid state triggers the change of the magnetic properties, including the ferromagnetic transition temperature from 5 to 22 K. We performed ⁵⁷Fe Mössbauer measurement in order to probe the microscopic states of iron ions in (SP)[Fe^IIFe^III(dto)₃] and have investigated the photo-induced effect on them. The sample without UV-irradiation shows the charge transfer phase transition between 200 and 70 K and the higher and lower temperature phases coexist below 70 K, whereas the UV-irradiated sample does not undergo the charge transfer phase transition and the higher temperature phase is stable between 200 and 6 K.     

Determination of the phenolic-group capacities of humic substances by non-aqueous titration technique

The phenolic-group capacities of five humic substances, such as, the Aldrich humic acid, the humic and fulvic acids extracted from a soil, the humic and fulvic acids extracted from a peat have been precisely determined by the non-aqueous potentiometric titration technique. The titration by KOH in the mixed solvent of DMSO:2-propanol:water = 80:19.3:0.7 at [K⁺] = 0.02 M enabled to measure the potential change in a wide range of pOH (=−log [OH⁻]), and thus to determine the capacities of phenolic groups which could not be precisely determined in the aqueous titration. The results of the titration revealed that the mean protonation constants of the phenolic groups were nearly the same for all humic substances and close to that of phenol in the same medium, indicating that each phenolic-group in the humic substances is rather isolated and is not electronically affected by other affecting groups in the humic macromolecule.     

Synthesis of chiral oxime ethers based on regio- and enantioselective allylic substitution catalyzed by iridium-pybox complex

The oxygen atom of oximes acts as a reactive nucleophile in the iridium-catalyzed allylic substitution of unsymmetrical substrates to give the branched oxime ethers. Among several chiral ligands evaluated, the iridium complex of pybox ligand having phenyl group catalyzed the allylic substitution of phosphates with high activity to form the branched oxime ethers with good enantioselectivities.     

Versatile synthesis of epicatechin series procyanidin oligomers, and their antioxidant and DNA polymerase inhibitory activity

Proanthocyanidins, known as condensed tannins or oligomeric flavonoids, exist in many edible plants and show various interesting biological activities. We have developed a simple and versatile method of synthesizing procyanidin oligomers consisting of (−)-epicatechin and (+)-catechin. This method is applicable to the synthesis of various 3-O-substituted oligomers. We report here the stereoselective and length controlled synthesis of [4-8]-condensed (−)-epicatechin series procyanidin oligomers. We described the details of the synthesis of an two tetramers, (−)-epicatechin-(−)-epicatechin-(−)-epicatechin-(−)-epicatechin and (−)-epicatechin-(−)-epicatechin-(−)-epicatechin-(+)-catechin (arecatannin A1), (−)-epicatechin pentamer and two 3,3″,3?-tri-O-galloyl trimers, (−)-epicatechin-(−)-epicatechin-(−)-epicatechin-3,3″,3?-tri-O-gallate and (−)-epicatechin-(−)-epicatechin-(+)-catechin-3,3″,3?-tri-O-gallate with the condensation method using TMSOTf as a catalyst. The ability of DPPH radical scavenging activity and DNA polymerase inhibitory activity of these oligomeric compounds were investigated.     

Total synthesis of cucurbitoside A using a novel fluorous protecting group

The first total synthesis of cucurbitoside A was achieved using a new fluorous N-phenylcarbamoyl (^FCar) protecting group. The ^FCar group was introduced into carbohydrates in high yield and was selectively removed with Bu₄NNO₂ without damaging other acyl protecting groups. The synthetic intermediates were easily isolated by fluorous solid-phase extraction.     

Tumescenamide C,an antimicrobial cyclic lipodepsipeptide from Streptomyces sp.

Tumescenamide C, a new cyclic lipodepsipeptide, was isolated from a culture broth of an actinomycete Streptomyces sp. KUSC_F05. Tumescenamide C was a congener of tumescenamides A and B, representing a sixteen-membered ring system, consisting of two proteinogenic and three non-proteinogenic amino acids, to which a methyl-branched fatty acid was attached. The planar structure was determined by spectroscopic analysis, while its absolute stereochemistry was determined by chemical degradation and asymmetric synthesis. Tumescenamide C exhibited antimicrobial activity with high selectivity against Streptomyces species.